This invention relates to a method for determining the crystalline quality of material of a semiconductor surface using light.
In manufacturing semiconductor devices, the surface of the semiconductor material in which the devices are fabricated must be substantially free of both physical and crystalline defects. A high degree of crystalline perfection is necessary to produce reliable devices having good electrical properties. In order to control the properties of such devices, it is necessary to be able to determine the quality of semiconductor material that is being used to make the devices.
The light reflectance of the surface of a semiconductor is generally dependent on the physical and crystallographic condition of the surface.
Physical surface damage such as scratches, pits and surface roughness, resulting from lapping and polishing procedures, can be detected by light scattering effects in the visible region of the spectrum for example, by the use of conventional lasers to scan the semiconductor surface. Similarly, the surface texture of homoepitaxial and heteroepitaxial films, prepared on various substrates by chemical vapor deposition (CVD), can also be detected in similar fashion. An example of particular importance is silicon-on-sapphire (SOS). Surface texture or "haze", observed visually because of light scattering, has been attributed in the past to inferior quality SOS material.
Crystallographic damage (or what may be also termed "lattice disorder"), which may also result from lapping and polishing procedures or may be present in homoepitaxial or heteroepitaxial semiconductor films such as SOS, is not easily detected by reflectance methods using visible light. This is due to the fact that the well known "optical" constants of a semiconductor, such as crystalline silicon, are not appreciably influenced by lattice disorder in the visible region of the spectrum. However, the optical constants of silicon are significantly influenced by lattice disorder at photon energies near 4.3 eV which corresponds to the well known X.sub.4 -X.sub.1 silicon transition. This transition occurs at a wavelength of about 2880 angstroms in the ultraviolet region of the spectrum. Thus, the light reflectance of silicon, which is a function of the optical constants, is sensitive to crystalline damage or lattice disorder in the UV region of the spectrum. Other semiconductors display similar reflectance properties at their corresponding characteristic wavelengths.
In view of the above discussion, it is clear that in the semiconductor field there is a need for a fast, nondestructive, quality control method for determining the crystalline quality of semiconductor materials.